1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium including a recording layer formed in a concavo-convex pattern.
2. Description of the Related Art
For a magnetic recording medium such as a hard disc, significant increase in areal density is conventionally achieved by various types of development that includes size reduction of magnetic particles forming a recording layer, change of material for the recording medium, and heightening precision of processing a head, for example, and further increase of the areal density is expected to continue.
However, problems such as side-fringes or crosstalk resulting from the limitation of the processing of heads or the spreading of magnetic fields have come to the surface, so that the conventional ways of improving the areal density have reached their limits. Thus, as a possible magnetic recording medium that can further increase the areal density, a discrete track magnetic recording medium has been proposed in which a recording layer is formed in a predetermined concavo-convex pattern and concave portions of the concavo-convex pattern are filled with anon-magnetic material (see Japanese Patent Laid-Open Publication No. Hei 9-97419, for example).
As a process technique for forming the recording layer in a predetermined concavo-convex pattern, dry etching such as reactive ion etching can be used (see Japanese Patent Laid-Open Publication No. Hei 12-322710).
Moreover, as means for filling a non-magnetic material, a deposition method such as a sputtering method, CVD (Chemical Vapor Deposition) method or an IBD (Ion Beam Deposition) method can be used. When such a deposition method is used, the non-magnetic material is deposited not only in the concave portions of the concavo-convex pattern but also on the upper surfaces of the convex portions. In addition, the surface of the deposited layer of non-magnetic material has a concavo-convex pattern that follows the concavo-convex pattern of the recording layer.
In order to obtain favorable magnetic characteristics, it is preferable that the non-magnetic material on the recording layer be removed so as to leave the non-magnetic material on the recording layer as little as possible. Moreover, in the case where the surface of the magnetic recording medium has a step, problems of unstable flying of the head, deposition of foreign particles on the magnetic recording medium, and the like may occur. Thus, it is preferable to flatten the surface of the recording layer while the excess non-magnetic material on the recording layer is removed. In order to remove the excess non-magnetic material on the recording layer and flatten the surface of the recording layer, a process technique such as a CMP (Chemical Mechanical Polishing) method, and oblique ion etching can be used. As the convex portions and the concave portions on the surface of the deposited non-magnetic material layer are smaller, it is easier to flatten the surface in a flattening process. Therefore, it is preferable to suppress the concavo-convex pattern on the surface of the deposited layer of the non-magnetic material to be as small as possible in the deposition process of the non-magnetic material.
In order to achieve this, a technique is known that deposits a non-magnetic material while a bias power is applied to an object to be processed (see Japanese Patent Laid-Open Publication No. 2000-311937, for example). In case of depositing the non-magnetic material while the bias power is applied, an action of depositing the non-magnetic material, and an action of etching the deposited non-magnetic material by gas or the like that is biased by the bias power, occur simultaneously. The non-magnetic material is deposited when the deposition action progresses more than the etching action. Etching tends to selectively remove the deposited non-magnetic material at a projecting portion thereof than at other portions, so that the projecting portion is etched faster than the other portions. Thus, due to this etching action, it is possible to suppress the formation of the concavo-convex pattern on the surface of the deposited non-magnetic film to be small in the deposition process of the non-magnetic material. Therefore, it is possible to flatten the surface of the deposited non-magnetic film efficiently and sufficiently in the flattening process.
However, in the deposition method with the bias power applied, the recording layer may be partially removed together with the non-magnetic material because of the etching action. This degrades the magnetic characteristics of the recording layer, thus degrading accuracy of recording and reproduction.
Moreover, in order to protect the recording layer in the flattening process, a stop film having a lower process rate in the flattening process may be formed on the recording layer. In this case, the non-magnetic material is deposited on the stop film. However, the stop film may be partially removed together with the non-magnetic material by the etching action during the deposition of the non-magnetic material. This damages the function of the stop film, thereby allowing the recording layer to be processed in the flattening process. Therefore, the magnetic characteristics of the recording layer are degraded.